Researcher Dr Kelly Hamby from the University of Maryland has previously described the incursion of spotted wing Drosophila (SWD, Drosophila suzukii) in the United States: “When SWD first invaded, growers and researchers scrambled to find quick solutions, which necessitated using insecticides…Outbreaks of pests that historically were not problematic have occurred in response to SWD management.”
Through a collaborative Australia-New Zealand research and extension approach we have been investigating how spotted wing Drosophila travels long distances, how quickly it would spread after an incursion, and the best methods to detect the fly. In our previous project update we highlighted the modelling work that has been carried out so far, which predicts that spotted wing Drosophila would spread down the eastern seaboard of Australia, as well as Tasmania, and the south west of Western Australia within approximately six years in the absence of control measures.
In this update we draw on a literature review by Plant and Food Research Australia and share how early overseas detections were made. We also recommend some simple preparedness actions that will support your farm and local industry in being ready to act if this fly were to be found in your region.
Thumbs down for this hitchhiker
We have now investigated circumstances surrounding first detections of spotted wing Drosophila in over 30 countries spanning North America, South America, and Europe.
Fast spread throughout regions and between countries has been supported by this fly’s ability to survive in warm and cool climates. Only one year after a confirmed 2008 detection of spotted wing Drosophila in California the fly had been found in 20 counties across the state, as well as the cooler climate states of Oregon and Washington, and the decidedly warm climate state of Florida.
How did it travel so quickly? Spotted wing Drosophila larvae make a home out of developing or ripe fruit until pupation. With the larvae hidden away, long range transmission is supported by movement of produce. In reviewing the academic literature, it was noted that South American researchers were able to rear spotted wing Drosophila out of imported blueberries purchased at a Sao Paulo grocery store – blueberries that had been grown in an entirely different Brazilian state.
Several first detections of spotted wing Drosophila overseas have occurred near fruit transit hubs. Examples of this include near a grocery store in Sweden, by a selling point for imported fruit in the Netherlands, and in a tourist area in Croatia. The first detection in Hungary was at a highway rest stop. Detections near major seaports have also been common, which may indicate a higher risk of entry and establishment near seaports.
When it comes to more modest expansion of the fly range within a region or country, the rate of spread observed overseas suggests that vehicles play a role, rather than flight-based spread (remember – this is a very small fly!).
What can we say about likely incursion sites?
The majority of early detections overseas have occurred in horticultural regions, although this may be a product of proactive trapping and grower vigilance, rather than the fly preferentially establishing in production zones. Indeed, past surveys have shown higher spotted wing Drosophila trap counts in wilderness (woodland) areas compared to cropping areas, and we cannot ignore those detections made at sites of fruit transit. The location of proactive trapping efforts or regions where awareness is high is likely to play a big role in where this fly is detected first if it does travel to Australia or New Zealand.
We can only speculate on likely incursion sites in Australia and New Zealand at this stage. Early detections made in Europe, South America and the United States in recent years were not necessarily at the site of the initial incursion. What we can say is:
- Our berry, grape and stone fruit production zones would be, on the whole, suitable for establishment;
- First detections of spotted wing Drosophila commonly occur on the coast;
- Based on how spotted wing Drosophila moves long distance (in imported fruit) urban areas are likely incursion sites;
- Imported fruit move through ports and airports, which have been common detection sites overseas;
- Wholesaler and retailer sites are important to consider – unsold imported fruit left in waste piles can present a risk;
- Detection of spotted wing Drosophila all year round may be possible in temperate areas of Australia and New Zealand.
Establishment obstacles – it all needs to go the right way for spotted wing Drosophila
Long range movement of imported fruit is the standout risk for bringing spotted wing Drosophila into Australia or New Zealand. If spotted wing Drosophila were to arrive via long range movement of fruit and subsequently establish, it would need to run a gauntlet first.
Catching an incursion early – what can you do?
Exotic pest incursions can be pretty stressful and disruptive. If spotted wing Drosophila were to be detected in a production zone, understanding how your farm can work with biosecurity authorities and minimise disruption of fruit sales from your farm or region is very important. For growers in high risk industries, such as rubus, strawberry and stonefruit, we have suggested some ways that you can plan and prepare through the checklist below. Hopefully your planning is never needed!
Farm and local preparedness for spotted wing Drosophila – action checklist
Staff understand how to identify spotted wing Drosophila adults or infestation:
- Circulate spotted wing Drosophila identification video
- Circulate Plant Health Australia spotted wing Drosophila fact sheet
A farm operating procedure for reporting a suspect spotted wing Drosophila infestation is in place:
- Source pre-emptive advice from your state Biosecurity Authority
- Train staff in internal procedure for logging details of an infested site, containing the site, taking a fruit sample and making a report
Trapping protocol developed and ready for execution:
- Identify best trapping locations (heavily wooded areas, wild blackberry stands, fruit waste sites)
- Develop data collection method with Biosecurity Authority
Farm biosecurity plan is up to date:
- Identify pest pathway risks
- Use your Industry Biosecurity Plan to decide on actions to minimise pathway risks (available from your industry body or Plant Health Australia)
- Ensure farm staff have read and follow the plan
Local industry understands the risk:
- Add spotted wing Drosophila as an agenda item for discussion at your next local grower group meeting
- Invite somebody from your Biosecurity Authority or Plant Health Australia to present on emergency response procedures to your local industry
- Take Plant Health Australia’s online biosecurity training
Local industry has agreed on emergency actions:
- Agree on local level actions if a detection is made
- Set up a local emergency response working group that can be ‘activated’ to act as an information source and trusted communicator (consider members from local government, agronomy groups, and influential community groups)
This project – ‘Improving the biosecurity preparedness of Australian horticulture for the exotic spotted wing Drosophila (Drosophila suzukii)’ MT17005’ – is a collaboration between Plant Health Australia, Plant & Food Research Australia, and cesar. This project has been funded by Hort Innovation, using the strawberry, raspberry and blackberry, cherry and summerfruit research and development levies and contributions from the Australian Government. Hort Innovation is the grower-owned, not-for-profit research and development corporation for Australian horticulture.